JPS5929922A - Construction of heat generating wire of heat generating body for ceramic glow plug - Google Patents

Abstract

PURPOSE:To increase the fastening force between the heat generating wire and ceramic insulator, suppress the heat generating wire to shift due to expansion and contraction of the wire itself, and consequently prevent the inner cracks from generating by a constitution wherein twisted wire is employed for the coiled heat generating wire embedded in the ceramic insulator. CONSTITUTION:The twisted wire construction consists in twisting two or three strands 1'-a, 1'- b..., each of which has a circular section and is made of resistance heat generating metal wire. The wire diameter is set based upon the resultant resistance value, which is necessary for twisted wire and calculated in accordance with heating conditions, the material of metal employed as wire, and the twisted wire construction (the number of strands and pitch of twist) and the like. Both ends of the coiled heat generating wire 1' are connected to leading-out electrodes 2-a and 2-b. Said wire 1' is embedded in ceramic powder mainly composed of silicon nitride. The heat generating body is constituted so that strong fastening force is produced between the ceramic insulator and the wire by biting the ceramic insulator in the valley-like recesses on the surface of the twisted wire when the insulator is sintered integral with the wire by means of a hot press. Due to the construction as mentioned above, the minute shifting due to the expansion and contraction of the heat generating wire caused by the tuning ON for energizing and OFF for deenergizing can be suppressed and consequently the generation of the inner cracks prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating wire structure of a heating element in a ceramic glow plug that is mainly installed in a diesel engine and is effective for preheating the inside of a cylinder or a sub-combustion chamber at the time of starting. Diesel engines have poor starting characteristics, especially at low temperatures, so a method is used to install a glow plug in the cylinder or auxiliary combustion chamber and heat it with electricity to raise the temperature inside the combustion chamber and improve the engine's starting characteristics. The glove 2 has a sheathed heater structure in which the heating wire coil is embedded in heat-resistant insulating powder and covered with a metal sheath. A so-called 72mic glow plug, which is embedded in a body and has no metal sheath as a heating element and has excellent heat conduction efficiency, has been used. That is, as shown in FIG. 1(a), the heating element is constructed by connecting lead-out electrodes 2'+2-b to both ends of a heating wire 10, and embedding it in a ceramic insulator 3.

By the way, the heating wire 1 of the conventional ceramic glow plug heating element is made of a single resistance heating metal wire with a circular cross section as the wire material, as shown in the cross-sectional views of main parts shown in FIGS. Because the surface of the heating wire is smooth and the bonding force of the bonding surface 4 with the ceramic insulator 3 is insufficient, 0N when energized
- Due to expansion and contraction due to repeated OFF cycles, slight movement occurs between the wire and the ceramic insulator 3, and internal cracks occur due to stress applied to the inside of the wire, increasing the resistance value of the heating wire and deteriorating the heat generation performance. It has been found that this may cause problems.

The present invention was made in view of the above-mentioned situation, and
The coil-shaped heating wire embedded in the ceramic insulator is replaced with a stranded wire instead of the conventional circular solid wire, and ceramic powder is bitten into the four parts formed on the surface of the stranded wire, thereby creating a heating wire in the ceramic insulator. The purpose of the present invention is to provide a ceramic glow plug heating element that increases the adhesion force between the heating wire and the insulator, inhibits movement of the heating wire due to expansion and contraction, and prevents the occurrence of internal cracks, thereby causing no deterioration in heating performance.

Figure 2 (A) is a longitudinal sectional view showing a part of a ceramic glow plug using the heating wire of the present invention, and Figure 2 (B) shows the state of adhesion between the heating wire of the stranded wire structure of the present invention and the ceramic insulator. FIG. 2C is a cross-sectional view of the exothermic line taken along line X--X in FIG. In the figure, reference numeral 1' indicates a heating wire, for example, wires 11a, 1/B having a circular cross section made of a resistance heating metal wire such as tungsten (W), molybdenum (Mo), or an alloy thereof (WMo). ,
...It has a twisted wire structure made up of two to six wires twisted together. In this case, the diameter of the strands is determined based on the required combined resistance value of the stranded wire calculated according to the heating conditions, the quality of the metal used, the stranded wire configuration (number of strands, twist pitch), etc. Both ends of the heating wire 1' are formed into a coil shape.

It is connected to lead-out electrodes 2-a and 2-b for energizing, and is embedded in ceramic powder mainly composed of silicon nitride, similar to the conventional example shown in Fig. 1, and hot-pressed. During integral sintering, the ceramic insulator is bitten into and filled into the valley-like recesses on the surface of the stranded wires, forming a heating element with strong adhesion. The lead-out electrode 'l-a is brazed to the metal outer cylinder 5 which is fitted into the outside (1111) on the side surface near the base end of the ceramic insulator 30, and the metal outer cylinder 5 is connected to the metal fitting 6.
On the other hand, the other hanging pole 2-b is soldered to the metal cap γ at the base end of the ceramic insulator, and is welded to this in advance. It is connected to the middle terminal to the outside through the lead rod 8 to form a current conducting path.

As can be understood from the above, the heating wire of the present invention of the heating element in the ceramic glow plug.

Due to the stranded wire structure, the valley-like recesses 9 shown in FIGS. The adhesion force at the bonding surface between the heating wire and the ceramic insulator becomes extremely strong, suppressing slight movement due to expansion and contraction of the heating wire due to ON-OFF during energization, and reducing stress generated inside the wire to prevent internal cracks. By preventing the occurrence of , it is possible to provide a ceramic glow plug with extremely stable heat generation performance and long life.

[Brief explanation of the drawing]

Figure 1 (A) is a longitudinal sectional view showing the heating element of a conventional ceramic glow plug, Figure 1 (B) is an enlarged longitudinal sectional view showing its main parts, and Figure 1 (C) is a longitudinal sectional view showing the heating element of a conventional ceramic glow plug. 2(a) is a vertical sectional view showing a part of the ceramic glow plug using the heating wire of the present invention, FIG. ) is a cross-sectional view of the exothermic line taken along the line X-X of the same figure (b). 1, 1'-- exothermic line, 1/a, i/,
b., strand, 2-a. 2-b... Leading electrode, 3... Ceramic insulator, 4
...Joint surface, 9...Concavity. Agent Patent Attorney Mamoru Takeuchi

Claims (1)

[Claims] Disposal of the heating element in a ceramic glow plug characterized in that the heating wire, which is embedded in a cylindrical ceramic insulator and is connected to a lead-out electrode provided at the base end and forms the heating element, has a twisted wire structure. Hot wire structure.